Microlens array with tailored sag profile

Abstract

An optical device includes a first array of emitters disposed on a substrate and configured to emit respective beams of optical radiation in a direction perpendicular to the substrate. A second array of microlenses is positioned on the substrate in alignment with the respective beams of the emitters, having respective sag profiles that vary over an area of the substrate. The second array includes at least first microlenses in a central region of the substrate and second microlenses in a peripheral region of the substrate, such that the first microlenses have respective first focal powers, while the second microlenses have respective second focal powers, which are less than the first focal powers.

The invention claimed is: 
     
       1. An optical device, comprising:
 a first array of emitters disposed on a substrate and configured to emit respective beams of optical radiation in a direction perpendicular to the substrate; and 
 a second array of microlenses positioned on the substrate in alignment with the respective beams of the emitters and having respective sag profiles that vary over an area of the substrate, the second array comprising at least first microlenses in a central region of the substrate and second microlenses in a peripheral region of the substrate, such that the first microlenses have respective positive first focal powers, while the second microlenses have respective negative second focal powers. 
 
     
     
       2. The device according to  claim 1 , wherein the sag profiles are defined such that the microlenses have respective focal powers that decrease gradually from the first focal powers to the second focal powers in a radial direction over the area of the substrate. 
     
     
       3. The device according to  claim 1 , wherein the sag profiles define respective tilt angles of the microlenses, and the tilt angles vary over the area of the substrate. 
     
     
       4. The device according to  claim 3 , wherein the tilt angles are greater in the peripheral region of the substrate than in the central region, whereby the microlenses refract the beams toward a central axis. 
     
     
       5. The device according to  claim 1 , wherein the substrate comprises a semiconductor chip, which is transparent to the optical radiation emitted by the emitters, and wherein the emitters are disposed on a first surface of the semiconductor chip and emit the respective beams through the substrate, while the microlenses are disposed on a second surface of the semiconductor chip, opposite the first substrate. 
     
     
       6. The device according to  claim 5 , wherein the microlenses are defined by a pattern of recesses etched into the second surface of the semiconductor chip. 
     
     
       7. The device according to  claim 1 , wherein the substrate comprises a semiconductor chip, and wherein the emitters are disposed on a surface of the semiconductor chip and emit the respective beams in a direction away from the substrate, while the microlenses are disposed over the emitters. 
     
     
       8. The device according to  claim 1 , wherein the emitters comprise vertical-cavity surface-emitting lasers (VCSELs). 
     
     
       9. The device according to  claim 1 , wherein the sag profiles are chosen such that the respective beams transmitted through the microlenses have respective foci that lie on a geometrical surface that is not flat. 
     
     
       10. The device according to  claim 9 , wherein the geometrical surface is curved. 
     
     
       11. The device according to  claim 10 , and comprising projection optics having an object plane that is not flat and which coincides with the curved geometrical surface. 
     
     
       12. The device according to  claim 11 , wherein the projection optics are configured to collimate the beams that have been transmitted through the microlenses. 
     
     
       13. The device according to  claim 11 , wherein the projection optics comprise a diverging lens. 
     
     
       14. The device according to  claim 11 , wherein the projection optics comprise a plastic singlet. 
     
     
       15. The device according to  claim 1 , and comprising projection optics, which are configured to collimate the beams that have been transmitted through the microlenses, and wherein the respective sag profiles define an astigmatism of the microlenses that corrects for an aberration of the projection optics. 
     
     
       16. A method for producing an optical device, the method comprising:
 forming a first array of emitters on a substrate so that the emitters emit respective beams of optical radiation in a direction perpendicular to the substrate; and 
 positioning a second array of microlenses on the substrate in alignment with the respective beams of the emitters, the microlenses having respective sag profiles that vary over an area of the substrate, the second array comprising at least first microlenses in a central region of the substrate and second microlenses in a peripheral region of the substrate, such that the first microlenses have respective positive first focal powers, while the second microlenses have respective negative second focal powers. 
 
     
     
       17. The method according to  claim 16 , wherein the sag profiles define respective tilt angles of the microlenses, and the tilt angles vary over the area of the substrate. 
     
     
       18. The method according to  claim 16 , wherein the sag profiles are chosen such that the respective beams transmitted through the microlenses have respective foci that lie on a geometrical surface that is not flat. 
     
     
       19. The method according to  claim 16 , and comprising configuring projection optics to collimate the beams that have been transmitted through the microlenses, wherein the respective sag profiles define an astigmatism of the microlenses that corrects for an aberration of the projection optics.